I have the ability to create my own generator function that returns a Generator. The type for this can be specified as
type Iterable = { [Symbol.iterator](): Generator };According to the documentation on Array, the method returns a "new array iterator object" which you can learn more about by visiting https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#the_iterator_protocol
type IterableBuiltIn = { [Symbol.iterator](): { next: any, value: any, return: any };
const array: IterableBuiltIn = [1, 2, 3];
for (const value in array) {
console.log(value);
}